In a wireless communication system, a base station may provide one or more coverage areas, such as cells or sectors, in which the base station may serve user equipment devices (UEs), such as cell phones, wirelessly-equipped personal computers or tablets, tracking devices, embedded wireless communication modules, or other devices equipped with wireless communication functionality (whether or not operated by a human user). In general, each coverage area may operate on one or more carriers each defining a respective bandwidth of coverage, and each coverage area may define an air interface providing a downlink for carrying communications from the base station to UEs and an uplink for carrying communications from UEs to the base station. The downlink and uplink may operate on separate carriers or may be time division multiplexed over the same carrier(s). Further, the air interface may define various channels for carrying communications between the base station and UEs, such as one or more control channels for carrying control signaling and one or more traffic signals for carrying application-layer data and other traffic.
In accordance with the Long Term Evolution (LTE) standard of the Universal Mobile Telecommunications System (UMTS), for instance, the air interface is divided over time into frames and subframes, with each subframe having two time slots. Further, the uplink and downlink channels are each divided over their frequency bandwidth into sub-carriers that are grouped within each slot into resource blocks. When a UE is positioned within coverage of a base station in such a system, the UE may register or “attach” with the base station on a particular carrier on which the base station is configured to schedule particular downlink and uplink resource blocks to carry data communications to and from the UE.
A recent revision of LTE known as LTE-Advanced now permits a base station to serve a UE with “carrier aggregation,” by which the base station schedules bearer communication with the UE on multiple carriers at a time. With carrier aggregation, multiple carriers from either contiguous frequency bands or non-contiguous frequency bands can be aggregated to increase the bandwidth available to the UE. Currently, the maximum bandwidth for a data transaction between a base station and a UE using a single carrier is 20 MHz. Using carrier aggregation, a base station may increase the maximum bandwidth to up to 100 MHz by aggregating up to five carriers.
When a base station provides a UE with carrier aggregation service, each aggregated carrier is referred to as a “component carrier.” In addition, one of the carriers may be deemed to be a “primary carrier” or “primary cell” (PCell) and each other carrier may be deemed to be a “secondary carrier” or “secondary cell” (SCell). In some scenarios, communication of control signaling associated with the bearer data may occur on a control channel of the PCell, whereas communication of bearer data may occur on the traffic channels of the PCell and one or more SCells.
In some wireless marketplaces, multiple wireless service providers may coexist, with each wireless service provider providing a wireless communication system. Each wireless service provider may be licensed by a regulatory agency to operate in one or more distinct, non-overlapping regions, or “bands”, of the radio frequency (RF) spectrum. For instance, in the United States, the Federal Communications Commission (FCC) holds regulatory authority over the RF spectrum for this purpose. Among the concerns and issues relating to operating in different regions of the RF spectrum is minimization and/or avoidance of RF emission “leaking” into one band due to transmissions originating from an adjacent or nearby band. To address this concern, a regulatory agency, such as the FCC, may set one or more requirements specifying allowable levels of power leakage for certain bands, while not necessarily prescribing how to achieve the specified levels. As one example, the FCC may require UEs operating on carriers that are in close proximity to emergency bands or the like to attenuate their uplink transmission power. Various design and engineering standards may be devised that specify procedures and protocols aimed (possibly among other purposes) at meeting such requirements.
One approach to controlling RF emission leakage is to implement an operational protocol by which a base station may signal to UEs in its coverage area an instruction or notification to attenuate their respective uplink transmission powers under certain circumstances, such as when operating on carriers in close proximity to emergency bands or the like. By way of example, in an LTE system, a base station may provide a network signaling (NS) value to UEs being served by the base station, and the NS value may correspond to an amount by which the UEs should attenuate their uplink transmission power. In one example configuration, for UEs operating on carriers where specific FCC requirements do not apply, the base station may provide, by default, a NS_01 value corresponding to zero attenuation. Accordingly, the UEs operating on those carriers may operate using a default maximum uplink transmission power. On the other hand, for UEs operating on carriers where specific FCC requirements do apply, the base station may provide a different NS value, such as an NS_03 value, an NS_04 value, or an NS_06 value, corresponding to a particular amount of attenuation (e.g., 3 dB, 5 dB, 10 dB, etc.) by which UEs should reduce their default maximum transmission power.